It is true that using single units is more reliable then multi-effects, but that doesn't mean that the multi-effect is unreliable. It is juz the expression of the sounds & the choice of setting in a single unit is wider.....
Pros & Cons.... If you were to use single unit, you might find yourself spending lots of cash collecting them, but it is worth the money (depends on what you buy). If you were to use multi-effects, although it isn't as good as single unit, the sound multi-effects offers isn't that bad after all. You can save lots of money if you were on budget plus the multi-effect are in one single piece...
I am using a multi effects (zoom GFX8), i find it not that bad.... Again it depends what you wants & how you see it.....
make a wise choice....
: 8)